1. Field of the Invention
The invention relates to radio frequency identification (RFID) technology, and in particular, to efficient writing of data into user memory of RFID tags.
2. Background Art
Radio frequency identification (RFID) tags are electronic devices that may be affixed to items whose presence is to be detected and/or monitored. The presence of an RFID tag, and therefore the presence of the item to which the tag is affixed, may be checked and monitored wirelessly by devices known as “readers.” Readers typically have one or more antennas transmitting radio frequency signals to which tags respond. Because the reader “interrogates” RFID tags, and receives signals back from the tags in response to the interrogation, the reader is sometimes termed as “reader interrogator” or simply “interrogator.”
With the maturation of RFID technology, efficient communication between tags and interrogators has become a key enabler in supply chain management, especially in manufacturing, shipping, and retail industries, as well as in building security installations, healthcare facilities, libraries, airports, warehouses etc.
RFID tags typically include a memory device for storing various items of information. In an agreement with the Automotive Industry, EPCglobal provided a definition to a previously undefined bit within the Protocol Control (PC) bits of a Gen 2-type tag memory word. The previously defined bit is bit 15 (hex) of tag memory bank 01 (also known as “EPC memory”). The new definition of this bit indicates whether or not any data is currently stored in tag memory bank 11 (also known as “user memory”). This bit is also referred to as a “user memory flag.” A “1” logic value for this bit indicates that user memory stores data. A “0” logic value for this bit indicates that user memory stores no data. In light of this new bit definition, two write operations will be required to write data into user memory of a tag. These write operations occur over two separate communications between a reader and the tag. A first write is required to write the data into user memory (memory bank 11), and a second write is required to set bit 15 (hex) of EPC memory (memory bank 01). The first and second write operations can occur in either order.
Because two write operations are required to different memory banks, the possibility exists that if the second write operation fails (for example, because the tag moved out of range of the reader), the user memory flag will not correctly indicate the state of user memory. For example, if the user memory flag is set by the first write operation, and the second write operation fails to write data into a previously-empty user memory, then the user memory flag will incorrectly indicate the presence of user data when no valid data is present. Alternatively, if the first write operation is used to write data into a previously-empty user memory, and the second write operation fails to set the user memory flag, then the user memory flag will incorrectly indicate an “empty” user memory, and the data written into user memory by the first write operation will erroneously be ignored by subsequent readers.
Thus, what is needed are ways to ensure proper writing and clearing of data in user memory of RFID tags.